M5, not a fine thread. This size is standard across bike brands. Check at your Local Hardware Store (LHS). Even the most expensive Allen head stainless steel bolts should be at most $.70 each. I could easily see a LBS selling you a $15.00 Fender Installation Kit.

Think about how you will secure the rear fender at the BB. The little clip on the fender might or might not latch into the chainstay bridge. It did on my Trek 610 (similar frame as yours), but did not on my Woodrup, which has a beefier chain stay. I used a Pclip on the Woodrup.

Ok, we have a lot of diversity of opinion, probably all with good reason. Go the your Ace or LHS, and buy one of each of those sizes. Take them home and see what fits. I would not assume there's English "cross" to the metric size. I know my bike (a 1984 Trek 610) threaded perfectly with metric bolts, so I'm pretty sure an English size isn't right for you. But I'm not sure if its M4 or M5. I do know it's the same as for my water bottle cage. You could take the water bottle bolt, test it in your fender eyelets, and if it's the same take it to the hardware store and say, "please give me four of these."

your welcome Bill those scews come with lots of defferent heads 3,4,5, mm allen and straigh and philips. most all braze on screws ar that size as well as most cleats. I don't know who suggested the nylon washers, not a bad ida, but velo orange sells some nice leather washers for fenders

your welcome Bill those scews come with lots of defferent heads 3,4,5, mm allen and straigh and philips. most all braze on screws ar that size as well as most cleats. I don't know who suggested the nylon washers, not a bad ida, but velo orange sells some nice leather washers for fenders

Hi, I think it was Nylok nuts, that once torqued grab and don't back off. But if we're bolting to threaded eyelets with the proper threaded bolt, we don't need any nut on the far end of the bolt.

I suppose one could use a leather or nylon washer to isolate vibration. I'm not sure the eyelet would be the best place for that, however.